Design Method of PWM AC/DC Flyback Converters
Designing Isolated Flyback Converter Circuits
From this point on, we start the design of an actual isolated flyback converter. First, we show a circuit diagram using the [PWM controller IC for AC/DC: BM1P011FJ] that was chosen for a case study.
In this sections and sections that follow, we will explain how to select the parts necessary for the circuit and a method for calculating the constants used. Therefore, the other sections also need to reference this circuit, by means of links that are provided for your convenience.
- Isolated Flyback Converter Basics
- Design Procedure
- Determining Power Supply Specifications
- Choosing an IC for Design
- Designing Isolated Flyback Converter Circuits
- Transformer Design (Calculating numerical values)
- Transformer Design (Structural design) － 1
- Transformer Design (Structural design) － 2
- Selecting Critical Components – MOSFET related - 1
- Selecting Critical Components – MOSFET related - 2
- Selecting Critical Components – CIN and Snubber
- Selecting Critical Components – Output Rectifier and Cout
- Selecting Critical Components – IC VCC related
- Selecting Critical Components – Setting up an IC and Miscellaneous
- Addressing EMI and Output Noise
This circuit is designed to satisfy the [Power Supply Specifications as a Case Study] that were established previously.
Power Supply Specifications as a Case Study
- Input voltage: 85 to 264 VAC
- Output: 12 VDC±5% / 3A 36W
- Output ripple voltage: 200mVp-p
- Isolation voltage: 3kVAC between primary and secondary
- Operating temperature range: 0 to 50℃
- Efficiency: 80% or higher
- No load input power: 0.1W or less
Through a filter, the input voltage undergoes rectification and smoothing in the full-wave rectifiers DA1 and C1. The rectified DC high voltage is input into the transformer T1 and switched by the switching transistor Q1. The output on the secondary side of the transformer T1 is isolated by an optocoupler, and it is fed back to the IC1 for the AC/DC converter IC. The feedback controls the switching transistor Q1 and regulates the output. Such is the overall structure of the circuit.
The other parts and circuits will be described in the succeeding sections.
・Calculation of part constants and important points in selecting parts will be explained using this circuit as an example.